Short-term anaesthesia is defined in terms of duration (allowing brief but what might be painful surgery), rapid recovery, metabolism and mode of administration. After a brief review of barbiturate narcoses, the authors study the electro-clinical features of anaesthesia under Althesin, Epontol and ketamine. For the first two, although there are some clinical differences, the E.E.G. effects are fairly similar with rapid onset of burst suppression. Recovery is rapid and its study (clinically, with psychomotor tests and E.E.G.) indicates that these drugs can safely be used with out-patients. Ketamine causes very specific alterations, both clinical (dissociative anaesthesia) and E.E.G. (diffuse and continuous theta). This drug is used particularly in painful operations; its use with out-patients would seem awkward.